An estimated 40%-70% of the causes of short and late mortality are related to immunosuppressive therapy following liver transplantation (12, 13). The available standard in most centers to monitor immune status relies heavily on drug levels, liver biochemistry and clinical events, which do not adequately assess the immune cells. The challenge in balancing the risks of under- and over- immunosuppression is further complicated by the lack of reliable means of predicting patients’ immunosuppressive needs.
Our proposed MICA is based on the weighting of each cell subpopulation in the whole lymphocytes, thus can give a thorough evaluation of the immune status. Different scores are closely associated with different immune responses and vice versa, which in essence reflect the immune status of liver transplant recipients. Hence, the scores vary as the percentages of lymphocyte subsets from the peripheral blood changes.
In our study, we first evaluated the immune state of the healthy individuals. HC of different age groups and gender were found to be in an almost balanced immune state in spite of slightly suppressed according to the mean scores. Nowadays, healthy individuals have been under a number of pathophysiologic stresses, such as hard work, fatigue, spiritual stress, intensive exercises, and sleep disturbances, which pertains to the piling up of biowaste produced by biochemical side-reactions (14–18). The consequential accumulation of metabonomic byproducts in human body will finally harm the immune system, therefore, leading to a subhealthy condition (19, 20). This is a state characterized by some disturbances in psychological behaviors or physical characteristics, or in some indices of medical examination, with no typical pathologic features (21).
Next, we found the immunity was greatly impaired in liver transplant recipients before surgery, especially in patients with benign diseases. Innate and adaptive immune dysfunctions are significantly compromised in patients with chronic liver disease on the waiting list as cirrhosis-associated immune dysfunction contributes to immune paresis and impaired anti-microbial response (22, 23). Therefore, patients with cirrhosis are at increased risk of infections due to impaired immunity and increased gut permeability leading to bacterial translocation in the setting of portal hypertension(24). On the other hand, bacterial translocation can lead to spontaneous bacterial peritonitis, and subsequent systemic inflammatory response syndrome, sepsis, and multiorgan failure, accelerating immune suppression (25). Whereas patients with malignant diseases on the waiting list usually have normal organ functions at our department. The possible explanation might be that only the anti-tumor function of lymphocytes are inhibited significantly in the tumor microenvironment to result in immune escape of malignant tumors (26, 27). Surprisingly, female patients had higher preoperative scores although there was no difference in healthy controls. This may be due to a higher ratio of malignant diseases in females (58.8%) than in males (47.9%).
Following liver transplantation the immunity is suppressed due to immune induction and maintenance. As a higher incidence of rejection within 28 postoperative days may enhance immunosuppressive therapy (28, 29), patients had the minimum scores. Then, there might be an immune homeostasis reached between the graft and the recipient, resulting in a gradual recovery of immunity.
Since the scores could be used to reflect the immunity of HC and patients we used the preoperative scores as an index to regulate the first dose of immunosuppressive agents. Tailored immunosuppressive therapy can be made as immunity varies among patients. Therefore, we should not pursue the target trough levels recommended by the guideline, which in fact is not proper for each liver transplant recipient. Although patients with low scores were treated with a less first dose of immunosuppressive agents, the similar recovery between the groups meant that regulating first dose of immunosuppressive agents via the scores may be an alternative.
Currently, ImmuKnow has been the only assay approved by FDA to quantify cell-mediated immunity by measuring the concentration of ATP from CD4+T cells (30). However, contradictory results have been reported in predicting acute rejection (7–9), which affect its wide spread usage. There have been repeated reports that both cellular immunity and humoral immunity play an important role in rejection following liver transplantation (31–33). The most commonly used immunosuppressive agents, such as cyclosporine and tacrolimus, only inhibit T lymphocytes such as CD4+T cells (34). Then, a possible explanation for above phenomenon is that ImmuKnow focuses on the cellular immunity. By only stimulating the cell-mediated immunity, the poor sensitivity may reflect ImmuKnow failing to recognize and therefore measure the contribution made by humoral immunity to rejection processes.
Acute graft rejection is a combined response of the adaptive (cellular immunity) and humoral immune system (secreted antibodies by activated B cells) in combination with the innate immune system (phagocytosis) (35–37), which are in response to various cell populations of our MICA. The lymphocytes clonally expand and differentiate at different timing and rates in case of acute rejection, which can accordingly lead to different scores. From this perspective, scores can predict the immune status, which were found to be the only significant independent risk factor. At the same time an increase in scores might also indicates acute rejection, which was proved by comparison of liver functions on postoperative days. After clonal expansion activated lymphocytes will cause organ damage, leading to increased levels of liver function. Therefore, the scores change theoretically a few days ahead of the liver function, allowing us to add the dose of immunosuppressive agents before the situation gets worse.
In conclusion, the MICA and MISS could be used as an alternative to reflect the immunity of healthy controls and liver transplant recipients as well as an index to regulate the dose of immunosuppressive agents.
The main limitation in this study is that it represents the experience of a single center. Future studies, preferably randomized controlled trials in multicenters, are needed to further validate our initial report.